To some, a smart home means greater energy efficiency —like appliances that respond to time-of-day pricing or motorized curtains that shut on hot days. To others, it’s whimsy — like waterproof speakers that blast “Immigrant Song” while propane torches ignite along the roofline. Either way, it’s cheaper and easier now to build the kind of smart, reliable home automation that has been promised for decades. New wireless protocols and cellphone-based interfaces make such installations extremely flexible. And by experimenting with next-gen technologies like gesture-based control and bio-engineered materials, you can turn your home into a research center that explores the technological limits of how easy, efficient, and fun your life can be.

Control Interfaces

When the Singularity comes, you’ll program your home with pure consciousness. Until then, you’ll need to tell any home automation system how to behave. Even in a smart home where actions auto-trigger based on occupancy sensors or weather patterns, you need some sort of setup screen or programming interface to define your system’s behavior. Some of the latest commercial graphical interfaces can provide a terrific front-end to custom hardware projects.

Cloud Service With a “cloud” interface, changes made on any web-connected device are routed back through the network to your home. Having the magic happen on a distant server means always-on status, cross-platform compatibility, and mobile access. Setting up these services — such as Digi’s iDigi Device Cloud, Verizon’s Home Monitoring and Control, Lowe’s Iris Smart Home System, or Xfinity’s Home Security — entails paying a fee, installing a home internet gateway, and logging into the company’s web page.

Home Computer With a PC or Mac wired into your system, it’s easy to make changes to your setup. You can do so from the computer room or outside the home using remote-access software. But if you’re energy-minded, remember that the machine must run continuously, with a load of at least 50 watts. That said, a computer-based interface offers the most flexibility for homebrew automation or security projects, like the Webcam Security System (page 44), especially if you’re conversant with C++.

Commercial Touchscreen Hardware/Software High-end automation systems such as AMX, Control4, and Creston use custom tablets that you carry around the house. These systems, and lower-cost packages, also offer iPad apps and sometimes iPhone and PC-tablet apps, as well.

DIY Control Screen and Web Interface You can make your own controller by connecting an Arduino microcontroller to buttons and a character LCD screen (page 54). Ladyada.net has a great tutorial on how to do this. With an Ethernet shield (or other interface) on the controller, you can run a simple web server that takes commands and reports device status via a private web page, and syncs up with other Arduinos by accessing the same server location. One limitation of putting a web server on the Arduino itself is that it will generally limit its access to the same network. So if it runs on a private port, the Arduino won’t also be able to pull data from the open web.

Protocols

Communications protocols dictate how well the automated devices in your home talk; they can mean the difference between a sprinkler system that turns off at the right time and one that floods the driveway. Some protocols send signals over electrical wires, others send them over the air. They all vary according to reliability, hackability, and security. The best opportunities are with protocols whose licensing bodies offer affordable developer kits for people who want to experiment.

ZigBee This protocol is based on the IEEE 802.15.4 standard for general-purpose wireless, plus some additions owned by the ZigBee Alliance (zigbee.org). It works on both 915MHz and the more common 2.4GHz frequency, with a range of 50 meters. Dumb nodes like sensors and switches sleep a lot, so they can run for over a year on battery power, while the rest of the system does the heavy lifting of routing the 250kbps data stream. This means you need to install at least one “coordinator” ZigBee node in a network (page 66). If you want to create the next ZigBee must-have, developer kits cost $150–$300.

Z-Wave This fast-growing standard (z-wavealliance.org) sends radio signals over the air on the 908.42MHz frequency, sometimes running afoul of cordless phones, but avoiding the increasingly crowded 2.4GHz space. It’s reliable, power efficient, and ranges between 30 and 100 meters depending on obstructions, but sends a meager 9.6kbps signal.

Insteon Compatible with the well-known X10 protocol, Insteon is the only system that sends signals on electricity lines and over-the-air radio at the same time, giving you double coverage. Many inexpensive devices for the reliable system are for sale on the Smarthome site (smarthome.com) and around the net. Want to mess around with it? A developer kit is $250.

X10 This powerline standard from the 1970s (x10.com) is the most mass-market option, although it can be sluggish and susceptible to interference: in one test, an X10 light switch inexplicably turned off whenever I played Stevie Ray Vaughan on a nearby stereo. There are no prefab developer kits, but you can read, write, and program X10 with an Arduino and a $15 plug-in device called a PSC05 (page 60). (Also note that inventor X10, Inc. is going out of business, resulting in dirt-cheap X10 gadgets coming to market as hacking fodder. For instance, a cheap light dimmer can be modified to control a motor.)

Wi-Fi Many very cool home automation gadgets, such as the Nest and Ecobee thermostats, and Belkin WeMo devices, use ubiquitous wi-fi. So you’d think the wireless network standard might be a good alternative for DIY home automation projects. But wi-fi, like networking standard HomePlug, is designed to move lots of data via TCP/IP, and it therefore demands wall current (or large batteries) and the processing muscle of a cellphone. Development boards cost $20 to $60.

Decentralized Control Some automation projects don’t need a communication protocol; they run on microcontrollers, or even just simple circuitry — imparting worm-like reflexes to a smart home, rather than a central nervous system. For instance, maker Ed Rogers used a vibration sensor to automatically close his windows when a train went by, and the Notification Alert Generator (NAG) reminds you of household tasks as you walk past (page 50).

Universal Powerline Bus UPB doesn’t have any developer boards, which puts a damper on things. Devices use the protocol by adding proprietary code to their firmware to send a radio signal on electrical lines using fat 40-volt pulses. The kicker? Setting up UPB requires expensive software tools, usually purchased by a contractor.

Physical Interfaces

Getting signals to zip around your home is one thing.The real challenge is ensuring that they trigger the intended actions. At the edge of the network, proximity, temperature, infrared (page 118), and other sensors provide inputs to the controller. And for outputs, devices need to translate commands into steps, such as turning on a 240-volt power supply or operating a window-blind servomotor, then report back on device status to confirm success of the mission. (All protocols except X10 have a feedback system built-in.)

Plug-In Switches The simplest modules plug in to wall power and control any device that you plug into them. All protocols have such wall warts (prices vary from $10 to $200) as well as receptacles you can install in-wall for a seamless appearance. You can also control an outlet from a microcontroller using the PowerSwitch Tail II, which simply takes a digital pin output (3–12V DC, 3mA–30mA) to switch an integrated 120V AC, 15A plug.

Built-In Control Devices All home automation protocols feature myriad gadgets and appliances with the built-in ability to receive and send signals. Screw a ZigBee or Z-Wave thermostat into the wall, for instance, and it becomes visible to the network instantly. Automation-ready devices run from mundane light switches and door locks to sprinkler systems and pet feeders.

DIY Protocol Control If you’re building an interface yourself, think of it as two parts: the protocol-compatible transceiver, and the physical hardware that performs the action. Transceivers for almost all the protocols are relatively affordable; for example, $25 XBee boards that use ZigBee and other protocols, or the $15 X10 PSC05.These connect via some interface to the physical layer, like servomotors that open blinds or turn locks, or actuators that turn on and off a water hose. The interface can be relay circuits, drivers, microcontrollers, or push button programmable prop controllers (aka programmable switches), as described in Keybanging (page 72). The Networked Smart Thermostat project (page 54) performs its physical actions by tapping into the standard four-wire control bundle used in forced-air
HVAC systems.

Using this basic recipe, makers have created a vast array of custom interfaces. Anything can control anything: home theater remote controls that “change the channel” on physical reality, ovens that start cooking dinner when Google Latitude shows that you’re getting close to home. In some ways, home automation is like cooking ossobuco — it’s not that hard to do on your own, but it entails a lot of prep time in the kitchen.